1. Field of the Invention
The present invention relates to an automatic gain controller (AGC) in an optical disc reproducing system, and more particularly, to an AGC for preventing peaking in an output signal of the AGC, and a method therefor, when a defect exists in a signal reproduced by an optical disc.
2. Description of the Related Art
An automatic gain controller (AGC) in an optical disc reproducing system such as a compact disc player (CDP) and a digital video disc player (DVDP) amplifies an optical disc reproducing signal reproduced from an optical disc to a signal having a uniform peak-to-peak voltage. The optical disc reproducing signal is input to the AGC after passing through a DC coupling capacitor.
When a defect exists in the optical disc reproducing signal, no signal is input to the AGC in the defect section due to the DC coupling capacitor. Therefore, the AGC amplifies the input signal by the maximum gain obtained by the AGC in the defect section. When a DC offset is present in the AGC, the AGC amplifies a DC voltage as well as an AC voltage. Therefore, the DC level of the signal output from the AGC changes in the defect section. When a normal input signal is input after the defect section, the DC offset level settles following a predetermined time period.
The voltage level of a control voltage for controlling the gain of the AGC, described below, becomes abnormal during the defect section. When a normal optical disc reproducing signal is input following the defect section, a peaking signal, in which the peak-to-peak voltage of an output signal is much larger than a desired voltage due to an abnormal control voltage, may exist. A section of the output signal corresponding to the DC level of the AGC becoming normal after the normal optical disc reproducing signal is input again is referred to as a peaking section. Data loss occurs during the peaking section.
FIG. 1 shows that a peaking signal is generated in an AGC output signal when a defect section exists in an optical disc reproducing signal. In FIG. 1, a first graph 2 shows the output of the AGC, a second graph 4 shows a control voltage for controlling the gain of the AGC, and a third graph 6 shows the DC level of the AGC.
Referring to FIG. 1, when a defect exists in the optical disc reproducing signal, a defect section T1, in which no signal is input to the AGC due to an external DC coupling capacitor, is generated. At this time, the gain of the AGC is maximized. In the defect section T1, not only the AC voltage of the AGC, but also the DC voltage of the AGC, is amplified. Referring to FIG. 1, the level of the control voltage 4 for controlling the gain of the AGC is more than 4V, which is abnormal, during the defect section T1.
Accordingly, when the normal optical disc reproducing signal is input again following the defect section, a section T2, in which the peak-to-peak voltage of the AGC output signal is much larger than a desired 1Vp-p voltage is generated, due to the abnormal control voltage. Data loss occurs in the section T2 in which the peaking signal exists